1. Field of the Invention
The present invention relates to a light source apparatus that may be utilized in laser processing or the like, and an optical module constituting a part of the light source apparatus.
2. Related Background Art
A light source apparatus (laser processing apparatus) used in laser processing or the like, guides light, which is outputted from a light source section, to an optical module by means of a guide section and emits the light to the outside of the light source apparatus from this optical module (emits light to an object). As the light source section, a laser light source is typically used, and a laser light source including an amplifying optical fiber may be used. In such a light source apparatus, reflected light generated in an object that is irradiated with a laser beam may return to the light source section through the optical module and the guide section. In this case, the light source section may suffer damage. In order to prevent such damage on the light source section, an optical isolator for preventing incidence of the returned light upon the light source section is preferably used.
Usually, the optical isolator is used for a single beam with transverse mode. The isolation in this case is described in Japanese Patent Application Laid-Open No. 05-224151 (Document 1), Japanese Patent Application Laid-Open No. 09-054283 (Document 2), Japanese Patent Application Laid-Open No. 61-058809 (Document 3), and the like. That is, the isolation is defined assuming a case where light from the backward direction (a backward propagating beam) is incident through the same optical path as the optical path through which light incident in the forward direction (a forward propagating beam) propagates after passing through the optical isolator. In this case, as described in above Documents 1 to 3, the backward propagating beam is not terminated inside the optical isolator, but is emitted from the incident end of the optical isolator with shifts in the emission position and emission angle. Just for this reason, the backward propagating beam will not be coupled with the light source that emits the forward propagating beam.
As disclosed in above Document 1, when a birefringent element included in the optical isolator is a plate type, then for the backward propagating beam emitted from the incident end of the optical isolator, only the emission position will vary. However, there is a limitation also on the shift in the emission position due to the birefringence and the like. In the case that a beam with a large mode field diameter or the like is used, the isolation may degrade. In this respect, as disclosed in above Document 2, when the birefringent element included in the optical isolator is wedge-shaped, then for the backward propagating beam emitted from the incident end of the optical isolator, the emission angle also differs from that of the incident beam. Accordingly, even when the mode field diameter is large, the degradation of isolation can be suppressed while the distance between an optical fiber for guiding the forward propagating beam and the optical isolator is secured. However, as described in above Documents 3, there is a limitation also on the birefringence, and the emission angle that enables separation is at most on the order of 1° relative to the optical axis.